Conventional automotive power supply systems include a voltage regulator, an engine-driven generator and a battery. The generator has field windings and provides an output current which is a function of the voltage across the field windings. The voltage regulator serves to maintain the output voltage of the generator in accordance with the voltage requirements of the battery by controlling the current flow through the field windings of the generator.
One problem associated with conventional power supply systems results from voltage regulator or field coil short circuit failures. When the voltage regulator fails short, a maximum field current is applied to the generator which causes maximum charging voltage to be applied to the battery regardless of its state of charge. The battery voltage then increases to approximately 19 VDC which leads to an over-charge condition. Vehicle warning lamps are also operated at excessive voltage and, if this condition is allowed to continue, may either burn out the lamps or severely limit the life of the lamps. The known prior art includes designing all electronic modules in the vehicle to operate at 19 VDC to ensure vehicle operation under an excessive voltage condition.
U.S. Pat. No. 4,543,521, issued to Morishita et al., discloses a device for detecting faults in a vehicle's charging system and displaying the detection result on a display. However, Morishita fails to disclose a method or system for controlling the generator once the fault is detected.